1. Field of the Invention
The present invention relates to a package structure of planographic printing plates and an interleaf paper for packaging said plates. More specifically, the present invention relates to an interleaf paper for packaging and protecting the planographic printing plates and the plate-making layer by being contacted thereto, and also relates to a protective structure for the planographic printing plates using the packaging material.
2. Description of the Related Art
In recently developed plate-making methods, planographic printing plates, such as photosensitive and heat-sensitive printing plates, are widely used in order to facilitate automation of plate-making.
A planographic printing plate is typically produced by a procedure comprising the following steps:
applying surface treatments, such as sandblasting, anode oxidation, and silicate treatment, to a substrate that is a sheet or a coil of aluminum or an organic polymer resin or the like;
applying a surface treatment such as chemical conversion treatment, either alone or in combination;
laminating thereon a visible light-exposure type or laser-exposure type exposure layer;
optionally providing over the exposure layer an oxygen-blocking resin layer to form a plate-making layer; and then
cutting into a predetermined size.
Planographic printing plates are generally packaged in a layered state, packed in a box and consigned. Therefore, at the time of packaging, the planographic printing plates and interleaf papers are usually layered alternately for the purpose of protecting the plate-making layer. Moreover, board paper for protection called ‘protector board paper’ is commonly disposed at (at least) one end facing in the thicknesswise direction of a package bundle formed by alternately layering the planographic printing plates and the interleaf paper. Then, the package bundle is wrapped in an interior paper.
When using the above-mentioned planographic printing plates, which are packaged by using interleaf paper and protector board paper, in an automatic plate processor or the like, since the interleaf paper and the protecting cardboard must be removed from the planographic printing plates, an automatic plate processor having an automatic plate feeding function, wherein removal of the interleaf paper and feeding of the planographic printing plates are automatically carried out, is widely used for improving the efficiency of plate-making work.
However, if the interleaf paper and the protector board paper are adhered strongly on the planographic printing plates, when using the aforementioned automatic plate processor, the Interleaf papers and the contact cardboards are supplied to the automatic plate processor without being peeled off from the planographic printing plates. Hence, problems such as stoppage of the automatic plate processor may arise.
Moreover, when removing the interleaf paper from the surface of the above-mentioned planographic printing plates and supplying the planographic printing plates to the above-mentioned automatic plate processor, the plate-making layer of the planographic printing plate and the interleaf paper rub together. This can cause the plate-making layer to adhere to the interleaf paper and separate the plate-making layer, a phenomenon also referred to as “film-peeling”.
An example of a proposed interleaf paper capable of solving the above-mentioned problem is recited in Japanese Patent Application Laid-Open (JP-A) No.2-25845. This invention proposes interleaf paper made of a synthetic pulp-mixed paper, which is produced with a heating and pressuring process.
Additionally, JP-A No. 3-36545 proposes a packing structure of a photosensitive printing plate (planographic printing plate) wherein at least one of interleaf paper and protector board paper having a water content of 8% or less is used.
The above interleaf paper and protector board paper showed a sufficient effect for protecting a planographic printing plate having a visible light exposing- or laser-exposure type plate-making layer by preventing separation of plate-making layer or film-peeling.
However, the interleaf paper disclosed in JP-A No. 2-25845 has a higher material cost since the interleaf paper is made of a mixture of a wood pulp and a synthetic pulp that is expensive in itself. Furthermore, the interleaf paper is necessarily manufactured separately from a conventional paper, and therefore, manufacturing cost of the interleaf paper also rises higher.
Moreover, recently, a photo-polymerizing type planographic printing plate is becoming employed commonly as a direct plate-making planographic printing plate wherein printing image is directly on its plate-making layer by a laser beam. The photo-polymerizing type planographic printing plate has a plate-making layer having a photo-polymerizing layer and a oxygen-blocking resin layer laminated over the photo-polymerizing layer. The photo-polymerizing layer contains a radical generating agent generating a radical by a light, an alkaline soluble binder, a polyfunctional monomer and/or a prepolymer. The oxygen-blocking resin layer is for protecting the photo-polymerizing layer from oxygen in the air.
Since the radical generated from the radical generating agent contained in the photo-polymerizing layer is easily eliminated by the contact with oxygen in the air, when the oxygen-blocking resin layer is damaged, the area of the photo polymerizing layer that is under the damaged layer contacts with oxygen and looses the photo polymerizability. Therefore, even when radiated by a laser beam, the above-mentioned area won't be photo-polymerized and leads to a defect such as a void after development.
In general, the above-mentioned oxygen-blocking resin layer consists essentially of a polyvinyl alcohol and therefore, the oxygen-blocking resin layer does not always have a sufficient mechanical strength and it can be easily broken by particles such as a filler contained in an interleaf paper.
Therefore, even by using the interleaf papers proposed in the above-mentioned prior arts for packaging photo-polymerizing type planographic printing plate, it could not be prevented completely breakage or damage of the plate-making layer such as the photo-polymerizing layer and the oxygen-blocking resin layer. Thus, the generation of void cannot be prevented completely.